Cellular Respiration

Who does cellular respiration?

All cells

Why do cells do cellular respiration?

• To produce ATP

• To break down a large glucose molecule to a smaller and easier to use chemical energy for cellular work

  • Making proteins, active transport

Aerobic Respiration

• The process where cells use oxygen to break down glucose into ATP

• Eukaryotes use mitochondria and prokaryotes use their cell membrane

• Rxn is the oxidation of glucose - large amount of energy must be released in small steps

• In the ETC, electrons are passed to successively more electronegative molecules with oxygen as the final electron acceptor

• Releases little bursts of energy along the way

Redox Reactions

Used to carry energy throughout Cellular Respiration

Mitochondria Structure

• Outer membrane: Smooth boundary that encloses the mitochondrion

• Inner membrane: Highly folded (to max out surface area!) membrane that contains the electron transport chain

• Cristae: Folds of the inner membrane that increase surface area

• Intermembrane space: Space between the outer and inner membranes where protons accumulate

• Matrix: Inner compartment containing enzymes for respiration

• Ribosomes: Found in the matrix; synthesize mitochondrial proteins

• DNA: Circular mitochondrial DNA located in the matrix

• ATP synthase: Enzyme embedded in the inner membrane that produces ATP

Electron Transport Molecules

• Electrons are transferred from hydrogen to oxygen via NAD+

  • Dehydrogenase enzyme removes 2 H atoms, delivers 1H+ and 2e- (the other H+ is released)

• NAD+ → NADH (NAD+ is reduced to NADH)

• NADH then delivers electrons to ETC

Glycolysis

• The splitting of sugar (glucose) into 2 pyruvate

  • Goes from 6C to 2 3C

• Occurs in the cytoplasm of eukaryotes and prokaryotes

• Can occur without oxygen

• Produces a net (4 is made by 2 is used) of 2 ATP via substrate level phosphorylation

• Reduces NAD+ to NADH (NADH now carries an electron and can move it to other steps; an electron carrier)

Pyruvate Conversion

• Occurs before the Krebs Cycle if oxygen is available

• Pyruvate (2 3C) enters the mitochondria and is converted to Acetyl CoA

  • Each gives off CO2 and reduces NAD+ to NADH

Krebs Cycle/Citric Acid Cycle

• Occurs in the matrix of the mitochondria

• Acetyl CoA enters the cycle

• Gives off 2 CO2 as a waste product

• Reduces NAD+ to NADH and FAD to FADH2

• Produces 2 ATP

• 9 steps of chemical reactions and repeats twice; reduction

Electron Transport Chain

• Electron carries (NADH and FADH2) release electrons into the chain

• Electrons are carried by proteins down the chain

• As they are passed along, the energy released fuels the pumping of protons across the membrane to create a gradient (active transport against the concentration gradient)

• Oxygen is the final electron acceptor

• Coupled with chemiosis at the end

Chemiosmosis

• Occurs in the inner mitochondrial membrane

• ATP synthase converts ADP+P into ATP

• Uses energy from the ion gradient to power the synthesis of ATP

• ETC pumps H= INTO the intermembrane space

  • H+ leaks back through ATP synthase by facilitated diffusion and finally goes with the concentration gradient

• Protons flowing through turn the rotor and catalyze ATP synthesis

• Produces about 26-28 ATP per molecule glucose

Energy Yield of Respiration

• Theoretical energy yield is 32 ATP per glucose for eukaryotes

• The actual energy yield is somewhat less due to inefficiency and other needs of the cell

Catabolism of Proteins and Fats

Lipids and proteins can also feed into cellular respiration. Fats are broken into glycerol which enters glycolysis and fatty acids are converted to Acetyl CoA while proteins are broken into amino acids that enter glycolysis, pyruvate oxidation, or the citric acid cycle after the removal of their amino groups

Lactic Acid Fermentation

An anaerobic process that converts pyruvate into lactic acid, regenerating NAD⁺ so glycolysis can continue producing ATP when oxygen is absent.

Alcoholic Fermentation

An anaerobic process that converts pyruvate into ethanol and CO₂, regenerating NAD⁺ so glycolysis can continue producing ATP when oxygen is absent.

ATP Structure Reminders

• ATP has more potential energy than ADP + P

• Most energy lies between the 2nd and 3rd phosphate bonds

Substrate-Level Phosphorylation

Transfers phosphate group directly to ADP

• Happens during glycolysis and the Krebs Cucle

Oxidative Phosphorylation

The rotation of ATP synthase squishes a free P onto ADP during ETC

Gluconeogenesis

Glycolytic and citric acid cycle intermediates can be reduced and used to form glucose through gluconeogenesis. The body keeps a constant supply of glucose by regulating digestion, storage, and release. Glucose from food enters the blood, excess is stored as glycogen in the liver, and when blood glucose is low, glycogen is broken down or glucose is made from other molecules through gluconeogenesis, keeping blood glucose levels stable.